The heart is enveloped within a tissue membrane structure known as the pericardium or pericardial sac. The pericardium consists of two layers, the fibrous pericardium and the parietal pericardium, which is a serous lining adjacent to the fibrous pericardium. In some instances reference is made to a third visceral pericardial layer, the epicardium, which is the layer on the surface of the myocardium. Between the pericardial sac and the surface of the heart is an intra-pericardial space. Approximately 15 to 35 milliliters of serous fluid fills the intra-pericardial space, providing lubrication and protection for the heart.
For patients in need of cardiac rhythm treatment (CRT), a minimally invasive pericardial approach to placing a stimulating lead (e.g., a chronic cardiac pacing lead) has recently been used as an alternative to transvenous and invasive surgery methods. In the pericardial approach, doctors access the intra-pericardial space to place a stimulating lead on the epicardial surface. Needle and needle-like tools are generally used to gain access to the intra-pericardial space.
For example, some of these tools employ a distal suction cup to stabilize the pericardial sac while a needle punctures the pericardial sac and enters the intra-pericardial space. However, there is difficulty maintaining a vacuum to stabilize the pericardial sac and the diameter of a percutaneous port in these tools must be sufficiently large (e.g., 18 French diameter or larger). Many other tools access the intra-pericardial space by grabbing and stabilizing the pericardial sac while a needle is advanced into the pericardial space. Such tools may grab the pericardial sac, for example, using clips or pinchers. However, such tools often encounter challenges to accessing the intra-pericardial space when obstructions to the pericardial sac are present. For example, the pericardial sac is covered in a layer of fat, which varies in thickness from patient to patient.
In another approach that is unaffected by the layers of fat surrounding the pericardial sac, doctors gain percutaneous access into the intra-pericardial space using a sub-xiphoid puncture technique employing an epidural Touhy needle, for example, a 17-gauge Touhy needle. Visualization techniques, such as fluoroscopy, MRI, echocardiography, or endoscopy are generally used to guide the needle to an implantation location within the intra-pericardial space and to guide positioning of the stimulating lead. Contrast media may be used during puncture to determine if the needle has passed through the pericardial sac and is correctly positioned in the intra-pericardial space. However, such techniques pose the risks of the needle puncturing the myocardium, entering the heart chambers, and causing excessive bleeding.
Specifically, for patients with a relatively normal pericardial sac, gaining access into the intra-pericardial space using a needle is difficult. This difficulty arises because: the pericardial sac is generally a thin tough connective tissue with little stretchability; the pericardial sac is slippery on, and slides over the heart wall; and the virtual space available for puncture provides little puncture room for pressing the needle into the pericardial sac. The term “virtual space” refers to the potential space between the two extreme limits of the epicardial surface and the pericardial sac. The challenges of accessing the intra-pericardial space can easily result in the heart wall being punctured, increasing the risk for tamponade (i.e., compression of the heart by an accumulation of fluid or blood in the pericardial sac).
Accordingly, there is a need in the art for a method and apparatus that will facilitate accessing the intra-pericardial space while reducing the risk of puncturing the heart wall.